An article in "Electronic Letters", May 1965, Vol. 1, No. 3, pp. 67-68, discloses a low-disparity binary coding system for transmitting a digital signal from a first to a second station over a transmission medium, including a sender unit which converts serial 8-bit words of said digital signal into low disparity serial 9-bit words, and a receiver unit which converts received serial 9-bit words back into the original serial 8-bit words. To the extent it may be useful in understanding and practicing the present invention, that article is hereby incorporated by reference.